Since the early 1950's, physiologists and clinicians have recognized that the hypothalamus of the brain controls all the secretory functions of the adenohypophysis. This control is neurohumoral, with specialized neurosecretory neurons in the hypothalamus producing special polypeptides, the effect and role of each of which is to trigger acutely and chronically the secretion of each pituitary hormone.
An inhibitory factor was earlier characterized in the form of hypothalamic somatostatin which inhibits, at the pituitary level, the secretion of growth hormone. In 1982, a corresponding hypothalamic releasing factor for pituitary growth hormone or somatotropin was isolated from a human islet cell tumor, purified, characterized and synthesized. When tested, it was found to promote the release of growth hormone(GH) by the pituitary. This peptide has the sequence: H-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser- Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu -Arg-Gly-Ala-Arg-Ala-Arg-Leu-NH.sub.2. Human hypothalamic growth hormone releasing factor (hGRF) has now been found to have the same structure. Bohlen et. al. Biochem. and Biophs. Res. Comm., 114, 3, pp. 930-936 (1983).